Referring to FIGS. 1-4, there is shown a conventional lens cap which comprises a disklike body 10 and a locking member 20 that is held to the body 10 so as to be radially movable. A pair of support blocks 11 is mounted on the body 10 in a parallel relation to a radius. Each of the support blocks 11 is provided with a retaining groove 12 and a guide surface 13 located over the groove 12. The surface 13 acts to guide sliding movement of engaging legs 21 (described later). A cutout 14 (FIG. 3) is formed in the peripheral portion of the body 10 of the cap between the grooves 12. The ends of the blocks 11 which are on the side of the center of the cap constitute retaining walls 15 that prevent the locking member from coming off radially. The body 10 of the cap further has protrusions 16 to which springs are held.
The locking member 20 has engaging legs 21 and limit surfaces 22 which are in contact with the guide surfaces 13. The legs 21 are fitted in the grooves 12 in the blocks 11 so as to be slidable along the grooves. The locking member 20 is further formed with recesses 23 in which compression springs 24 are received. Each one end of the springs 24 abuts on the protrusions 16 to bias the locking member 20 in such a direction as to protrude from the body 10 of the cap.
The engaging legs 21 have anchoring portions 25 at their front ends, the anchoring portions being brought into engagement with the walls 15. The legs 21 are resilient enough to be capable of deforming to positions at which the anchoring portions 25 no longer engage with the walls 15, as shown in FIG. 4, when the locking member 20 is mounted to the body 10 of the cap. Spaces 26 are formed to allow this deformation.
Thus, in the prior art lens cap, the locking member 20 is always urged to protrude by the action of the compression springs 24. The protruding end of the member 20 is confined to the position at which the anchoring portions 25 bear on the retaining walls 15. In order to mount the cap to a lens, the locking member 20 is pushed inwardly with a finger until it covers the lens. Then, the locking member 20 is released. A locking portion 27 formed at the front end of the locking member 20 is engaged into a screw thread formed at the lens barrel to prevent the locking member 20 from coming off.
The engaging legs 21 of the prior art lens cap can preferably be deformed readily with a small force, as shown in FIG. 4 when the body 10 of the cap and the locking member 20 should be assembled easily. However, when the force to retain the lens should be increased, it is desired that the force exerted by the compression springs 24 be increased. Unfortunately, these two requirements have been difficult to satisfy at the same time using the prior art structure. More specifically, when the engaging legs 21 are made easily deformable to facilitate the assembly operation and the force exerted by the compression springs 24 is increased to augment the retaining force, the locking member 20 readily comes off the body 10 of the cap. Especially, when the locking member 20 is pressed inward fully against the action of the springs 24 and then the member 20 is released suddenly, or when an impulsive force is applied to the locking member 20 from outside, the engaging legs 21 are deformed, as shown in FIG. 4, and will disengage the body. When the force exerted by the springs 24 is made strong, the locking member may be prevented from coming off the body by making the legs 21 not easily deformable. However, this will render the assembly operation difficult, and creates the possibility of plastic deformation of the legs 21 or damage to them during assembly operation.